There have been lots of improvements since the 4.5.x series, though there are more features in 5.0.x (and therefore more code) we now do more lazy loading plus we switched to jetty server side which is a huge performance enhancement over tomcat.

Simply that 'the memory increases on tab click' kinda doesn't mean much, as loading more code can very well mean more memory usage. BTW Safari & FF are much faster at JavaScript rendering. Plus your workstation & server specks play a role too...